In order to convert electrical energy into kinetic energy, in addition to other structural forms of electric motors, so-called “induction machines” or “three-phased machines” are used. Induction machines may include a stator with a ring-shaped arrangement of so-called “phases,” which can generate temporally variable magnetic fields, and thereby can set into rotation a magnetic rotor, for example, an armature with a permanent magnet. Induction machines, for example, permanent magnet synchronous machines (PSM) or asynchronous machines (ASM), are employed in various applications, such as hybrid cars, electric cars, servo drives, machine tools, etc. With such induction machines, intermediate voltage circuit inverters (WR) are frequently used for the generation of supply voltages for the individual phases. Upon an error in the machine or in the inverter, one of the phases of the machine can be interrupted. If the machine continues to operate, this may lead to fluctuations in the turning moment. The document WO 2010/004239 A1 discloses a method in which a synchronous machine with several phases may continue to be operated even upon the failure of a phase. In doing so, however, in some operating cases of the machine, the phase currents can be very large, such that damages to the machine may arise, for example damages to the semiconductor components found in the inverter that are used to govern the voltages for the remaining phases.
In some applications, the machine may be switched off in the event of an error. Welchko, Jahns & Lipo (IEEE Power Electronics Letters, Vol. 2, No. 4, December 2004) disclose a method for the interruption of phase currents upon the occurrence of an error in synchronous machines with permanent magnets. This approach may be undesirable in some applications, for example, for a steering system or an electric car, since a sudden switching off of the engine in a vehicle requires the attention of the vehicle's driver, and this may result in accidents.
In order to be able to continue to put the machine in operation upon the event of a failure and the phase interruption that arises from this, in the alternative, a redundancy in the inverter or in lines of the machine may be used. However, these solutions may bring about additional complexity, additional volume and high costs. This may be impractical in a provided installation in a vehicle, as often only little space is available here, and, with greater quantities produced, the additional high costs can multiply.
As such, it is desirable to create an improved concept for controlling an induction machine, such as a PSM, upon the failure of one phase.